CBSE Class 11 Physics Important Questions with Solutions for 2025-26 exams

Physics in Class 11 is all about curiosity and logic, understanding why things happen the way they do. From motion and forces to thermodynamics and waves, every concept builds the foundation for Class 12 and entrance exams like JEE and NEET.

To master this subject, you don’t just need to read, you need to practise. That’s where these Class 11 Physics Important Questions come in.
They help you:

• Strengthen your basics from each chapter.
• Revise formulas and derivations in a structured way.
• Prepare effectively for both theory and numerical questions.

Whether you’re solving these questions chapter-wise or downloading the free PDF for offline practice, this guide ensures smart, focused preparation for your Physics exams.

Chapter - wise Most Important Questions For Class 11 Physics

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Class 11 Physics Important Questions with Answers

Q1. What is the difference between scalar and vector quantities?

Ans. Scalar quantities are physical quantities that have only magnitude but no direction. examples: mass, temperature, energy, time, and speed. Vector quantities have both magnitude and direction. Examples: velocity, acceleration, force, displacement. 

Vectors obey vector addition rules like the triangle law, while scalars follow simple algebraic addition.

Q2. State Newton's First Law of Motion.

Ans. Newton’s First Law, also known as the law of inertia, states that an object remains at rest, or if in motion, continues to move with uniform velocity in a straight line unless acted upon by an external force. For example, passengers lurch forward in a bus when brakes are applied suddenly due to inertia of motion.

Q3. Explain the principle of conservation of momentum.

Ans. The law states that in an isolated system (no external force), the total momentum before and after a collision remains constant.
Mathematically:
Example: In a bullet–gun system, momentum lost by the bullet equals momentum gained by the gun (recoil).

Q4. What is work done by a force? Give a formula with an example.

Ans. Work is done when a force applied on a body displaces it in the direction of force or its component.

Formula: If , W = Fd (maximum). If , W = 0 (no work).
Example: Lifting a 2 kg book vertically by 1.5 m:
W = mgh = 2 × 9.8 × 1.5 = 29.4 J.

Q5. Define gravitational potential energy.

Ans. Gravitational Potential Energy is the energy possessed by a body due to its position in a gravitational field.
For example, a 1 kg object placed 10 m above ground has PE = 98 J.

Q6. State Ohm’s Law and its significance.

Ans. Ohm’s Law: Current through a conductor is directly proportional to the potential difference across it, provided temperature and other conditions remain constant.
Significance: Helps in analysing circuits, designing electrical devices, and calculating resistance. Example: If V = 10 V and R = 5 Ω, then I = 2 A

Q7. What is the principle of superposition of waves?

Ans. When two or more waves overlap in a medium, the resultant displacement is the algebraic sum of displacements due to individual waves. Applications: interference of light waves, sound beats.

Q8. Describe simple harmonic motion (SHM).

Ans. SHM is a periodic motion where the restoring force is directly proportional to displacement from equilibrium and directed opposite. Equation:

Q9. What is the Doppler effect?

Ans. The apparent change in frequency/wavelength of a wave when the source and observer are in relative motion.

• Approaching source - higher frequency.
• Receding source - lower frequency.
  Example: Changing pitch of an ambulance siren when it passes by.
  Applications: astronomy (redshift), radar, ultrasound scanning.

Q10. State the laws of reflection and refraction.
Ans.

• Reflection: (i) Angle of incidence = Angle of reflection. (ii) Incident ray, reflected ray, and normal lie in the same plane.
• Refraction: (i) Incident ray, refracted ray, and normal lie in the same plane. (ii) Snell’s law: . Example: bending of stick in water.

Q11. Explain SI unit of solid angle.

Ans. Solid angle is measured in steradian (sr). It is the angle subtended at the centre of a sphere by an area equal to square of radius. If area A = r², then solid angle Ω = 1 sr.

Q12. What is a " free path"?

Ans. The average distance travelled by a gas molecule between two successive collisions. It depends on temperature, pressure, and size of molecules. Higher temperature increases mean a free path.

Q13. Derive the expression for acceleration due to gravity at Earth’s surface.

Ans. From Newton’s law:
where M = Earth’s mass, R = Earth’s radius.

Q14. Problem: Planet X has an angular diameter of 35.72″ at a distance of 824.7 million km. Find its diameter.

Ans. Converting 35.72″ = 1.73 × 10⁻⁴ rad.
D = θ × d = 1.73 × 10⁻⁴ × 8.247 × 10⁸ km ≈ 1.43 × 10⁵ km.

Q15. What is elasticity? Explain elastic limit and plastic behaviour with examples.

Ans: Elasticity is the property of a material to regain its original shape and size after the deforming force is removed. When a force is applied, the body deforms, but if it returns completely to its initial state, it is said to behave elastically. The elastic limit is the maximum stress that a material can withstand and still return to its original shape after unloading. 

Beyond this point, permanent deformation sets in. This is called plastic behaviour. For example, a steel wire stretched within its elastic limit returns to the same length after the load is removed. However, if the stretching force is too high, the wire will not regain its original length and will show plastic deformation. A contrasting case is clay, which shows almost no elasticity and deforms permanently under stress.

Q16. Define stress and strain. State types and SI units.

Ans. When an external force is applied on a body, internal restoring forces are set up within it. The restoring force per unit area is called stress. If a force acts normally on an area , stress is given by:

Its SI unit is Pascal (Pa). Stress quantifies the internal force resisting deformation.
Strain is the ratio of the change in dimension to the original dimension. For example, in the case of stretching, strain = ΔL/L. It is dimensionless.

Types of stress: (i) tensile/compressive stress, (ii) shear stress, (iii) bulk stress.
Types of strain: (i) longitudinal, (ii) shear, (iii) volumetric.

Q17. State and explain Hooke’s Law.

Ans: Hooke’s Law states that, within the elastic limit, the stress produced in a material is directly proportional to the strain: . Thus , where is Young’s modulus, a constant that measures stiffness of the material. 

The law is valid up to the proportional limit. Beyond this, the stress strain relation is non-linear, and permanent deformation may occur.

Q18. Derive expression for Young’s modulus.

Ans: Consider a wire of original length , cross-sectional area , stretched by a force . The extension produced is ΔL.

• Stress - F/A.
• Strain - ΔL/L.

Therefore, Young’s modulus. SI unit: Pascal.

Physically, Y represents the material’s resistance to deformation. Higher Y indicates greater stiffness (steel), while lower Y means more flexibility (rubber).

Q19. Define bulk and shear modulus.

Ans: Bulk modulus (K): Ratio of normal stress (hydrostatic pressure) to volumetric strain. Formula: . A negative sign shows that an increase in pressure decreases volume.

Shear modulus (G): Ratio of shear stress to shear strain. Formula: , where x is lateral displacement and h is height of the body. Both are measured in Pascals. These constants describe how a material responds to uniform compression or tangential force.

Q20. What is Poisson’s ratio?

Ans: When a rod is stretched, it contracts laterally. The ratio of lateral strain to longitudinal strain is called Poisson’s ratio (ν). It is given by ν = - (lateral strain)/(longitudinal strain). For most solids, 0 < ν < 0.5. Steel has ν ≈ 0.3. Rubber has ν close to 0.5. It gives an idea of how materials deform in perpendicular directions under stress.

Q21. State relations among Y, G, K, and ν.

Ans: In isotropic solids:

• Y = 2G(1+ν)
• Y = 3K(1-2ν)

These relations connect the three elastic moduli and Poisson’s ratio, allowing calculation of one if others are known.

Q22. Explain stress–strain curve of a ductile material.

Ans. The stress–strain curve typically has these regions: (i) Linear proportional region where Hooke’s law holds, (ii) Elastic region where deformation is reversible, (iii) Yield point where large strain occurs with little increase in stress, (iv) Strain hardening region where stress again rises, (v) Ultimate tensile strength (maximum stress), (vi) Necking and fracture. 

The area under the curve up to the elastic limit is called resilience (energy stored per unit volume). The total area under the curve till fracture is toughness (energy a material can absorb before failure). A clear sketch is often drawn in exams.

Q23. Derive expression for elastic potential energy in a stretched wire.

Ans. Work done in stretching a wire = average force × extension = (1/2)FΔL. Hence energy stored U = ½ FΔL. Per unit volume: u = ½ σ ε = σ² / (2Y). This expression is used to calculate strain energy density in materials.

Q24. Why does steel exhibit more elasticity than rubber though rubber can be stretched more?

Ans. Elasticity is not about how much a material can stretch, but how well it regains its original form. Steel has a very high Young’s modulus (≈2×10¹¹ Pa), so even small stresses produce very little strain. It resists deformation strongly and returns fully when the stress is removed. Rubber, though stretchable, has low Y (≈10⁶–10⁷ Pa), so it is less elastic in the true scientific sense.

Q26. State Pascal’s Law with applications.

Ans: Pascal’s law states: In a fluid at rest, pressure applied at one point is transmitted equally and undiminished in all directions. This principle is widely used in hydraulic lifts, hydraulic brakes, and presses. For example, in a hydraulic car lift, a small force applied on a small piston can lift a heavy car using a larger piston, since F1/A1 = F2/A2.

Q27. Derive expression for excess pressure inside a soap bubble and liquid drop.

Ans: For a liquid drop (one surface), excess pressure p = 2T/r, where T is surface tension, r is radius. For a soap bubble (two surfaces), p = 4T/r. This is derived by balancing the inward force due to surface tension and outward force due to internal pressure.

Q28. State and explain Newton’s law of cooling.

Ans: Newton’s law of cooling states that the rate of loss of heat of a body is directly proportional to the difference between the body’s temperature and the surroundings, provided this difference is small. Mathematically: dT/dt = -k(T - T_env). It explains practical cases like cooling of hot water in a room.

Q29. What is thermal expansion? Types?

Ans. Thermal expansion is the phenomenon of increase in size of a body due to rise in temperature.

• Linear expansion: ΔL = α L ΔT.
• Areal expansion: ΔA = β A ΔT.
• Volumetric expansion: ΔV = γ V ΔT.

Here, α, β, γ are coefficients of expansion. Examples: expansion gaps in bridges, bimetallic strips in thermometers.

Why You Should Download CBSE Class 11 Physics Most Important Questions?

As exams start nearing, students try to adopt the best strategy to prepare for the exams to achieve good marks. Math is one of those subjects that gives phobias mostly. To help students achieve the target, incorporating “Most Important Questions Practice” in the exam strategy is a vital step for many reasons.

• To have a deep understanding of topics in Class 12, understanding the topics from Class 11 will help in creating a strong base.
• These questions are curated to highlight the essential topics and principles and help students get the main idea behind that concept.
• Most Important Questions provide extra help and are important reference material to prepare for exams.
• If any students want to appear for competitive exams like JEE, NEET, or any other exam, the most important questions will help in aligning with the exam pattern and strategy.
• You can curate a more effective study plan by shortlisting important topics.
• These questions will help you boost your confidence for the board exams.

CBSE Class 11 Most Important Questions will help students cover all the major topics and understand that chapter. At Educart, we have pledged to help students with the right material and help them in scoring their dream scores. We hope that you practice the above most important questions of mathematics and achieve your dream marks in it.

FAQs

Q1. How many marks are usually asked from Class 11 topics in Class 12 Physics exams?

Ans.  Around 25–30% of the Class 12 board syllabus is based on Class 11 concepts, so revising them is crucial.

Q2. How should I prepare numerical questions in Physics?

Ans. Focus on understanding the underlying concept first. Then, practise similar problems repeatedly to build speed and accuracy.

Q3. Are derivations important for the Class 11 exam?

Ans. Yes. Derivations often carry 3–5 marks and also help you recall formulas easily during problem-solving.

Q4. How can I memorise formulas effectively?

Ans. Use flashcards or sticky notes for daily revision. Group formulas by chapter and concept to make them easier to recall.

Q5. Which chapters are most scoring in Class 11 Physics?

Ans. Motion in a Straight Line, Work, Power and Energy, Thermodynamics, and Gravitation are among the most scoring chapters.